I have a DIY wet dry with a 1000gph mag drive, but my overflow only does about 550gph so I put a ball valve on the outlet to control the flow. is this ok for the pump?
That is the proper way to do it in my opinion. Plus it's more dwell time for the water in the filter media instead of wasting the pumps output by restricting it.
Just return the water in the same place it does now from the tank. All you need to do is remove the ball valve out of the line it's in now. Then put a T fitting in it's place, run one end up to the tank and place the ball valve on the other end. Run the pipe/hose from the ball valve to the same place your current overflows drain into the sump. Then just open the ball valve until the output that is reaching the tank matches the output of your overflow. The rest will just get filtered again.
Ok, next chance I get to home depot ill buy some more tubing and a T. what is everyone's fail safe if their DIY overflow fails or gets clogged? im worried ill have about 15gallons from my sump all over my dining room
I dont know of any magical fail safe. I think was most of us to is overbuild the overflow so we are sure that it will handle the flow. Things are going to get partially clogged, it's part of the game. You need to make sure the overflow accounts for that. You might want to look for a smaller pump. Is this on the 20G planted tank?
You can do it with a float switch in the tank. If the level rises to high it cuts power to the pump. Just need a proper float switch / relay inline with the pumps power.
The other option is to drill a secondary overflow higher than the current one, likely not an option...
The other thing you can do as a free precaution is to not set the flow of the pump to the maximum the overflow can flow. This way if it does clog a bit it doesn't automatically begin to overfill the tank. The water level will just rise a bit and you'll notice the clog before it gets to bad.